The present invention relates to an apparatus for hydraulically adjusting the blades of an impeller of an axial-flow fan.
Modern axial-flow fans are regulatable work machines that convert mechanical energy into kinetic energy. The regulation of the axial-flow fans is effected via the speed or the angle of inclination of the blades. If during operation the blade position is to be able to be varied, the blades must be secured to a supported shaft, the spindle. The alteration of the blade position is generally undertaken hydraulically. For this purpose, a hydraulic adjustment or displacement mechanism is mounted on the impeller of the axial-flow fan. Such an adjustment mechanism is essentially comprised of a hydraulic adjustment cylinder, which rotates at the fan speed, and of a stationary oil delivery element, to which the oil supply lines are connected.
Due to the centrifugal forces of the blade caused by the rotation, enhanced by the geometrical shape of the blade profile, a torque, which acts as a restoring torque, results about the longitudinal axis of the spindle. If the adjustment mechanism fails during the operation, then the blade, due to this restoring torque, changes position in an abrupt manner, and the fan can no longer maintain pressure and conveying quantity. To prevent a change in position of the blades, counterweights can be mounted on each blade, generally however on the spindles, that more or less precisely compensate for the restoring torque. The drawback of such an approach is that the additional counterweights, due to the centrifugal force, effect a considerable overloading of the spindle mounting and make the impeller significantly heavier.
It is an object of the present invention to embody an apparatus of the aforementioned general type for the adjustment of blades during operation of the fan in such a way that even where there is a power failure the blade position can be maintained in the last position prior to such power failure until, by switching over the power, another control unit can take over the position regulation of the adjustment device.